Toast oven having at least five heating elements

ABSTRACT

A countertop multi-function oven. The oven, comprising: an internal compartment; a door for the compartment; at least five heating elements; the fifth heating element being located between two top heating elements; a controller coupled to the heating elements for providing a variable wattage; a user interface coupled to the controller, wherein upon user operation of the interface an oven mode is selected from one or more predetermined oven modes.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is divisional of application Ser. No. 13/443,837, filed10 Apr. 2012; which is a divisional of application Ser. No. 12/500,608,filed 10 Jul. 2009; which claims benefit of Australian ProvisionalApplication No. AU 2008903560, filed 11 Jul. 2008.

FIELD OF THE INVENTION

The invention relates to toaster ovens and more particularly to atoaster oven with variable power heating elements and versatile usercontrol over the operation of those heating elements.

BACKGROUND OF THE INVENTION

A toaster oven is used for a variety of cooking and food heating tasks.A toaster oven will be used, for example, for toasting a wide variety ofbreads (including frozen bread, bagels and pizza), baking cakes, andbroiling meats (grilling).

Handling the aforementioned tasks successfully requires powerful heatingelements and temperature control over these heating elements that issophisticated and versatile. In turn, easy and versatile control overthe heating elements is facilitated by a user interface that permits auser to utilise the various functions of the oven in a convenient andsafe way.

Details in the construction of a toaster oven are contained in theApplicant's co-pending Australian Provisional Application No. 2008901884which is incorporated herewith, in its entirety, by reference.

OBJECTS AND SUMMARY OF THE INVENTION

It is an object of the invention to provide a toaster oven having fouror more heating elements that can be controlled to perform a variety oftasks.

It is another object of the invention to provide a toaster oven havingheating elements that can be run at two or more power settings.

It is a further object of the invention to provide a toaster oven havingan easy to use and intuitive user interface that clearly distinguishesbetween the oven's toasting functions and its other functions.

According, a toaster oven is provided with four or more heatingelements. At least some of the elements are controlled in such a waythat the power output of the elements can be varied.

BRIEF DESCRIPTION OF THE DRAWING FIGURES

In order that the invention be better understood, reference is now madeto the following drawing figures in which:

FIG. 1 is a perspective view of a toaster oven in accordance with theteachings of the present invention;

FIG. 2 is a schematic cross section of a toaster oven in a toastingconfiguration;

FIG. 3 is a schematic cross section of a toaster oven in a bakeconfiguration;

FIG. 4 is a schematic cross section oven in a broil configuration;

FIG. 5 is a front elevation detail of a toaster oven showing a userinterface and oven door details;

FIG. 6 are front elevation details of the interface illustrating toastfunctions;

FIG. 7 is a front elevation detail of a portion of the interfaceillustrating bake functions;

FIG. 8 a is a schematic circuit diagram of a toaster oven in accordancewith the teachings of the present invention;

FIG. 8 b is another schematic circuit diagram of a toaster oven inaccordance with the teachings of the present invention;

FIG. 9 is a perspective detail of the arrangement of the oven's fiveheating elements;

FIG. 10 is an underside plan view of the top middle element's shield;

FIG. 11 is a side view of the arrangement depicted in FIG. 9;

FIG. 12 is an embodiment heating element;

FIG. 13 is a detailed schematic diagram of the printed circuit boarddepicted in FIG. 8;

FIGS. 14A, 14B, and 14C are schematic diagrams of the cycles of AC powerdelivered to the elements in an oven according to the teachings of thepresent invention;

FIGS. 14D and 14E are schematic diagrams illustrating alternative ACwave shapes;

FIG. 15 is a graph illustrating oven temperature over a durationassociated with a bake mode;

FIG. 16 is a graph illustrating oven temperature over a durationassociated with toast mode cycles; and

FIG. 17 is a graph illustrating oven temperature over a durationassociated with several bagel mode cycles.

BEST MODE AND OTHER EMBODIMENTS

As shown in FIG. 1, a toaster oven 100 comprises a thermally insulatedhousing 101 that defines an internal heating compartment 102. In thisembodiment, the compartment 102 is accessed through a door 103 with atransparent front panel 104. The door 103 is hinged, horizontally, alongits lower edge to a lower margin of the compartment 102. The door'shandle 105 is adapted to support the door, when it is fully open, on thesame horizontal surface that the oven's legs 106 rest on. A verticalpanel 107 on a front surface of the housing and adjacent to the door 103provides a user interface comprising a graphic display 108 and a numberof user controls, as will be discussed below. The internal compartmentfurther comprises three opposing pairs of fixtures 109 for supportingthe one or more removable racks 110. Details in the construction of atoaster oven are contained in the Applicant's co-pending AustralianProvisional Application No. 2008901884 (PCT/AU2009/000465) which isincorporated herewith in its entirety, by reference.

In the embodiment depicted in FIG. 1, the internal compartment 102 isheated by five quartz heating elements 120. As will be explained, threeof the quartz heating elements 120 are located adjacent to the ceilingor top of the compartment 102 and two of the elements are located alongthe floor or bottom of the compartment 102.

In this specification we refer to quartz heating elements, but it willbe noted that the invention can use many types of heating elementincluding stainless steel calrod, tungsten, halogen etc.

For toasting and where maximum power is desired, an element orcombination of all or some elements may be run at its full capacity.When, for example, baking or warming temperatures are required, anelement or combination of some or all elements need to deliver lowerpower in a way that is consistent with the needs of e.g. baking. Thepresent technology is adapted to deliver, at a macroscopic level (onethat can be sensed by a person, e.g. seen or felt) intermediate power.This means the technology creates, for at least a period of time thatcan be observed by a user, an appearance of a continuous power levelthat is somewhere between full and off. This is to be distinguished fromother oven element powering configurations where an element is cycled orturned on and off from full power to no power throughout a cookingcycle. This common prior art method achieves a form of intermediateheating, but the quality of e.g. baked goods suffers because of theintensity of the full power portion of the cooking cycle. The prior artform of intermediate heating also produces undesirable thermalovershooting of the desired target temperature. In particularlypreferred embodiments, the gentle, continuous, even heating preferred bybakers (for example in the baking of cakes) can be achieved throughoutall (or a significant or visible portion of) a cooking time by reducingthe amplitude of or “chopping” the AC wave form, or by omitting ordeleting or suppressing cycles of the AC waveform of the power suppliedto the heating elements, using triacs or cycling relays or otherelectronic components in the circuitry associated with some or allheating elements (but not necessarily the top central element 220). Inthis way, at least at a macroscopic or sensory level, the elementappears to be delivering what is defined here as true intermediatepower, a level of heat that is, for a user appreciable time,intermediate—less that the full power output of the element but morethan zero power. This true intermediate power can be combined with fullpower, no power and other true intermediate power settings during acooking cycle. True intermediate power is akin to electronic dimming ofthe heating element, as seen in lighting devices.

As shown in FIG. 2, the internal compartment 102 contains five quartzheating elements. The ceiling 200 of the internal compartment isconfigured to optimise even toasting. The central part 201 of theceiling is relatively flat. A curvature is provided in the ceiling, bothbehind 202 the rear element 203 and in front of 204 the front element205. The front curvature 204 extends downwardly toward a small flatstrip 206 that is lower than the central flat area 201. A short bevelledsection 207 extends across the top edge of the opening into thecompartment, terminating at the strip 206. The bevelled portion 207makes user access into the interior of the compartment easier.

FIG. 2 also illustrates that the interior floor 208 of the compartmentis protected by a removable crumb tray 209. The crumb tray 209 alsoincludes curved reflective portions in front of the front lower heatingelement 210 and behind the rear lower heating element 211. The crumbtray 209 is preferably flat between the forward curved reflectiveportion 212 and the rear curved reflective portion 213.

As will be further explained, an optimisation of the oven's versatilityand performance is achieved by providing five heating elements andutilising at variable wattages according to the mode of operation. (Insmaller or more economical versions of the oven of the presentinvention, the optional top central element may be omitted). In thepresent examples, the device is presumed to be running on 120 volt AC.It will be understood that values expressed in these examples, in watts,need to be adjusted accordingly when other line voltages are used. Inthe example provided in FIG. 2 it can be seen that the oven has a topset of three heating elements being, a top front element 205, a topcentral element 220 and a top rear element 203. The top front and rearelements are preferably operated in unison. In some embodiments, the topfront and rear elements 205, 203 are 450 watts and the middle element220 is 550 watts. In other embodiments, better performance is achievedby installing a 520 watt element in the top front position 205, a 380watt element in the top rear position 203 and a 550 watt element in thetop central position 220. In preferred embodiments, both of the lowerheating elements 210, 211 are 450 watts and operated in unison. As willbe explained, the top central element 220 and the bottom elements 210,211 may be shielded. In particularly preferred embodiments, the lowerelements and the top elements (but not necessarily the central element220) are current controlled or regulated with triacs to further vary thethermal output of the elements. In order to address safety andregulatory concerns (and as will be explained with reference FIG. 8) itis preferably not possible to operate the oven's top central element 220at the same time that the bottom elements 210, 211 are operated. Whenthe top central element 220 is on, both lower elements 210, 211 are off.When the lower elements 210, 211 are on, the top central element 220 isoff.

Toast Configuration

As shown in FIG. 2, uniform toasting of a wide variety of breads isachieved quickly by utilising four of the five heating elements 121.

In the example of FIG. 2, all of the oven's elements are on except forthe top central element 220. The other four elements 205, 203, 210, 211are operated at their maximum wattage. This produces the maximum glowingradiation for effective toasting. When used as a toaster, the oven'srack 110 is located in the middle position. As suggested by FIG. 5,instructions for using the rack in the middle position are printed on oradjacent to a corresponding location 501 on the oven's door.

In preferred embodiments the toaster oven uses the maximum availablewattage, limited by local regulatory or power limitations. In the US andCanada this is 1800 watts of power, shared equally between the top andbottom elements. In Australia this is 2400 watts.

Bake Configuration

As shown in FIG. 3, the toaster oven 100 may be used as an oven orconvection oven. When used as an oven, the top central heating element220 is not used but other heating elements 205, 203, 210, 211 are. Inthis configuration or mode, the rack no is preferably located in thelowest rack setting. The motorised convention fan 301 is preferably setto a default state of “on” although it may be defeated according to theoperation of the user controls on the control panel 107. In particularlypreferred embodiments, the gentle heating preferred by bakers (forexample in the baking of cakes) can be achieved by reducing theamplitude of or “chopping” the AC wave form, or by omitting or deletingor suppressing cycles of the AC waveform of the power supplied to theheating elements, using triacs or cycling relays or other electroniccomponents in the circuitry associated with both of the top and bottomheating elements (but not necessarily the top central element 220). Thisform of true intermediate power can be used continuously through acooking cycle or used intermittently with another true intermediate orzero power interval or combined with, for example, a pre-heating portionof a cooking cycle using full power for an initial time, to bring theoven up to the correct cooking temperature.

Broil or Grill Configuration

As shown in FIG. 4, the toaster oven 100 of the present invention may beused as a broiling or grilling device. In this configuration or mode,the rack 110 is preferably located in the uppermost position within thecavity 102. When the grilling or broiling cycle is selected by a user,all three top elements are used, preferably at their full power setting.However, any and all top element can be triac controlled, in unison, toprovide more precise power delivery. As previously mentioned, the topcentral element may be omitted in smaller or more economicalembodiments. As will be further explained, it is preferred that the topcentral element 220 (if present) be shielded. Accordingly, a perforatedmetal shield 401, is interposed between the element 220 and the foodbelow it. In preferred embodiments, the rack no is higher in the broilposition than in the toast position. The utilisation of three heatingelements above the rack assists in providing an even spread of heat.With only two elements, the oven would have a cool spot toward themiddle of the rack. The utilisation of the third element 220 enables thedelivery of an even heat. The use of the perforated shield allows somedirect radiation to pass through it. In special cooking configurationsor modes such as for melting cheese on toast, the intensity of theelements, particularly the forward and rear upper elements can bereduced by using triacs and the supply of true intermediate power (aspreviously explained) so that, for example, the toast doesn't burnbefore the cheese is melted. Further details concerning the variouscooking modes will be provided below.

User Interface

A user interface panel 107 is provided on the front of the toaster oven100. The user interface panel further comprises a graphic display area502 and various user operable controls 503. In preferred embodiments,the user controls are located directly below the graphics display 502.

The graphics display area 502 comprises a vertically arranged list ofcooking modes 504 and a moving arrow or indicator 505 that tells theuser which mode has been selected. In the example of FIG. 5, the modesinclude toast, bagel, bake, roast, broil, pizza, cookies, re-heat andwarm. The various modes and their functions will be explained below. Thegraphics display area 502 also comprises a toast shade selectionindicator 506. The indicator 506 shows schematic representations oftoasted bread, one light 507 and one dark 508. The user selections are,in this example, seven in number and small icons 509 in conjunction witha moving arrow or indicator 510 provide visual feedback to the user ofthe selected toast shade. The display area 502 further comprises anupper alphanumeric portion 511 and a lower alphanumeric portion 512. Theupper alphanumeric portion 511 is used to indicate, for example, anumeric value of the toast shade selected by the user (when the toastmode has been selected) or, an oven temperature (for example when thebake function has been selected). The lower alphanumeric portion 512 canbe used to indicate the number of slices of bread that the user hasselected (when the toast mode has been user designated), a pizza size,or the time remaining in a cooking cycle (for example when the bake modehas been user selected).

The user operable controls 503 provide the user with an easy way to makeselections or preferences, and provide inputs to the oven's processor inrespect of the various modes and user preferences within modes.Importantly, the primary modes designated in the vertical list 504 areselectable by a rotary dial 513 which is located in vertical alignmentand preferably below the list 504. Rotation of the mode dial 513 changesthe oven's functionality and the selected mode is indicated by themoving arrow 505. In this example, the start/cancel button 514 islocated directly below the display area 502 and adjacent to the modedial 513. The mode dial 513 allows the user to select one of a number ofdifferent modes or functions. However, within each of these modes, theuser is able to express various preferences. Thus, the two largestrotary selection dials are the temperature/darkness control dial 515 andbelow it, a time/load size dial 516. The upper dial 515 allows the userto adjust the cooking temperature, for example, adjusting the defaulttemperature associated with any particular mode upward or downward. Thissame dial 515 allows a user to select the selected shade or darkness oftoast when the unit is in a toast mode. When the toast mode has beenselected with the dial 513, rotation of the upper ortemperature/darkness selecting control 515 results in the appropriatemovement of the arrow or indicator 510. Rotation of the lower ortime/load size control 516 allows the user to adjust, before or at theinception of a cooking cycle or during it, a selected time or thedefault time specified by the unit's microprocessor. However, when theuser selected function is the pizza or toast function, rotation of thetime/load size dial 516 results in commensurate changes to the loweralphanumeric indicator 512 that relate to load size, such as number ofslices or pizza size. In preferred embodiments, the temperature/darknessdial 515 and the time/load size 516 are of equal size and located inproximity. Both may be operated during a cooking cycle so as to makeadjustment mid-cycle. The interface panel 107 also includes a button orcontrol 520 for the user selection or de-selection of the convection fanfeature. The convection fan feature preference is only available incertain modes. The interface panel 107 also includes a control or button521 that allows the user to toggle any displayed temperature fromFahrenheit to centigrade or centigrade to Fahrenheit. A frozen foodcontrol or button 522 is also provided. As will be explained, selectionof the frozen food preference allows the total cooking time to accountfor frozen foods (when this feature is enabled in a mode).

Examples of the way information is displayed in the graphics displayarea 502 are depicted in FIG. 5 and FIG. 6. As shown in FIG. 6, thefunction list 504 in conjunction with the indicator 505 show the userthat the toast mode has been selected. The upper alphanumeric area 511in conjunction with the symbolic display 506 indicates that the user hasselected a darkness or shade of 4. The lower alphanumeric area 512indicates that the user has selected four slices using the time/loadsize dial 516. Once the mode and preferences have been established, theuser presses the start/cancel button 514 and the display changesaccordingly. The resulting display, particularly the lower alphanumericdisplay area 512 displays the remaining cooking time 601 rather than thenumber of slices that have been selected. If the user had also selectedthe frozen food control button 522 the lower alpha numeric display area602 would show the user that more time had been added to the toastingcycle. A graphic icon and the word “frozen” 605 within the display area502 also provide feedback to the user that the frozen food preferencehad been selected by use of the frozen food control or button 522.

As shown in FIG. 7, when the user selected bake mode has been requested,the default temperature of 350 degrees Fahrenheit is displayed in theupper alphanumeric display area 511 and a default time, e.g. 30 minutesis displayed in the lower area 512. In preferred embodiments,utilisation of the bake function results in a default selection of theconvection feature and the same is indicated within the display area byan icon and/or text 701.

Circuitry

FIG. 8 a and FIG. 8 b show typical schematic circuit diagrams Boo forimplementation of the electronic control of the elements and fan. Inthis example, the oven's functions are controlled by an integratedcircuit 801. In this example, separate sub-circuits are provided forboth of the bottom elements 802, the middle top element 803, the fan 804and the front and rear top elements 805. An overload or storm protectionsub-circuit 806 is provided across the input power leads. Thesub-circuit 806 includes an optional thermal fuse 840, a noise filtercapacitor 841, a varistor 807 to absorb power surges and a PCB fuse 808as a back-up against the failure of the varistor 807. In the sub-circuit802 associated with the bottom elements, a triac 807 is protected by aheat sink 858. The triac is used as an electronic relay and currentcontroller (e.g. for delivering true intermediate power) in the controland regulation of both of the bottom heating elements 809, 810. Aresistor and capacitor 811, in series, and located across the outputs ofthe triac 807 absorb high frequency noise that may be produced from theoperation of the triac. The triac 807 can be used to switch the bottomelements on and off as well as regulating their current draw and thermaloutput with methods such as “chopping” or suppressing the AC wave form,many times a second (for true intermediate power, or otherwise) toreduce the effective or average wattage, as required. The sub-circuit805 for the top elements is similar to the sub-circuit for the bottomelements 802. The sub-circuit 803 for the middle top element 820, inthis embodiment does not use a triac, but it may. Instead or as well asa triac or other current regulator, it uses a relay 821 so as to createa toggling between the operation of the top middle element and the pairof bottom elements 809, 810. Thus, it becomes impossible (in thisconfiguration) to operate both the middle top element 802 and the bottomelements 809, 810 together. This optional toggling feature eliminatesthe need for a current fuse. The e.g. 20-60 watt fan 830 for theconvention feature is operated with a triac 831 but does not require ahigh frequency noise filter.

A thermistor 870 located in the oven provides temperature feed backinformation to the processor 801. Thus the processor can compensate oradjust (by reduction) the time calculated to cook based on the internaloven temperature of the oven at the time when the Start button 514 ispressed. This happens for automatic functions such as Toast, Bagel, andPizza as will be explained. The thermistor 870 is preferably locatedbehind a thin aluminium pressed shell or bubble at an upper portion ofthe back or sides of the oven, and is embedded in heat-sink paste.

An alternative circuit is depicted in FIG. 8 b. In this example, asingle triac 807 or other current regulating device is used to controleither the top middle element or the bottom elements. This is done byrouting the regulated output 880 of the triac 807 to the relay 821. Thusoperation of the relay delivers the regulated output to either thebottom elements 809, 810 or the top middle element 820 (but not both thebottom elements and the top middle element).

Elements and Shielding

As shown in FIG. 9, each of the oven's five quartz heating elements isprotected from accidental breakage. For example, the front and back topelements are located between and above a pair of stainless steel rods903. The top middle element 904 is physically protected by a radiationshield 905. The shield 905 is formed from metal and is shaped as agenerally “U” shaped or arcuate channel. As better shown in FIG. 10,various perforations 1000 are provided along the length of the shield905. The perforations 1000 are provided in three longitudinal rows 1001,1002 and 1003. The rows 1001, 1003 along the edges 1004 of the shieldare generally equally spaced and equally sized and provide only modestblocking of the intense radiant energy emitted by the heating element.In the example of FIG. 10, the perforations of the middle row 1002 areequally sized but irregularly spaced. The centre group 1005 ofperforations are further apart when approaching the centre of theshield. The middle row's outer perforations 1006, 1007 are spacedtogether more closely than the middle perforations 1005 and arepreferably evenly spaced. Thus, the central portion of the heatingelement is more shielded than the ends. This prevents a formation of ahot spot underneath the middle of the top middle element 905.

Because of the combined effects of the radiant and convection output ofthe lower elements, special shielding has been devised to providephysical protection of the elements in combination with the eliminationof hot spots associated with the lower elements. As shown in FIG. 11,the lower heating elements 1101, 1102 are both located below andlaterally of an adjacent stainless steel rod 1103. In addition, thelower elements 1101, 1102 are physically protected by an inverted “U”shaped, unperforated shield 1104. In this example, the shield 1104 ofthe lower elements is located above and within the upward projecteddiameter of each element. The shields 1104 are canted so that one lowerback or rear side edge 1105 is closer to the adjacent element than anupper front side edge 1106.

It will be appreciated that within the confines of a relatively smalloven compartment, a heating element that produces uniform heat acrossits length will produce a distribution of temperature within thecompartment that is uneven. Particularly with regard to shorter cookingtimes, operation of a uniform heating element will produce a temperaturein the middle of the oven that is hotter than the temperature close tothe side walls. This dilemma may be addressed by varying the pitch orspacing of the coils within the quartz heating element in the mannerdisclosed by FIG. 12. As shown in that figure, a quartz heatingelement's internal coil 1200 may contain, along its length, regions ofdifferent pitch or turn spacing. In the example of FIG. 12, the lengthof the coil 1200 can be thought of as having been subdivided into sixportions of generally equal length 1201, 1202, 1203, 1204, 1205 and1206. The outer most portions 1201, 1206 have the smallest or finestpitch (tightest spacing between adjacent turns). The central twoportions 1203, 1204 have the greatest spacing between adjacent turns andmay have equal pitches. The intermediate portions 1202, 1205 having turnspacing that is closer than the central portions 1203, 1204 but farther(greater or coarser pitch) than the outer portions 1201, 1206.

Further Discussion of the Toaster Oven's Modes

Toast Mode

The toast mode is user selectable with the mode dial 513. The toast modeis intended to be used with the rack 110 in the middle position. Inpreferred embodiments, the top middle element 220 is not used but theother elements are. The fan is not used and full power (preferably 1800watts or 2400 W where allowed by local authorities) is delivered to theremaining four elements. The time/load size dial 516 can be used toreceive a user preference of between 1 and 6 slices. The default settingis preferably four slices. Using the aforementioned wattage, toastingtimes vary between about 165 seconds for 1 slice (at the lowest browningsetting) to about 420 seconds (for six slices at the maximum browningsetting). The convection feature is turned off and the circuitry doesnot allow the user to activate the convection feature. When the frozenfood function is selected with the frozen food button 522 extra time isadded to the normal cycle time. By way of example, fifteen seconds isadded for one or two slices. Twenty seconds is added for three slices orfour slices. Thirty seconds is added for five slices and thirty fiveseconds is added for six slices.

The thermistor 870 in the oven may provide oven temperature feed backinformation that allows the processor 801 to compensate for the internaltemperature of the oven, by reducing the cooking time as required.

Bagel Mode

When the bagel function has been selected, the cooking cycle issubdivided. A first portion of the cooking cycle (e.g. two minutes and30 seconds) is cooked using 1800 watts of power. Thereafter, the poweris reduced, for example, to 1450 watts. In the first portion of thecycle, all of the elements are used except for the top middle element.Thereafter, all of three top elements are used but the bottom elementsare not used. In the bagel mode, the defaults are four slices and abrowning setting of 4 (out of 7). Cooking times vary from about 205seconds (for one bagel half at the lowest setting) to about 375 seconds(for six bagel halves at the highest browning setting). When the frozenfood preference is selected, extra time is added to the normal cookingtime. For example, 25 seconds is added for one bagel half and anadditional five seconds is added for each additional half, resulting inan additional 50 seconds when six slices or bagel halves are selected.When using the bagel function, the convection feature preferablydeactivated and prevented from being selected.

The thermistor 870 in the oven may provide oven temperature feed backinformation that allows the processor 801 to compensate for the internaltemperature of the oven, by reducing the cooking time as required.

Bake Mode

The maximum cooking time when the bake mode has been selected is about 2hours. In the bake mode, the convection fan default is “on”. The topmiddle element is preferably “off” and a total power of about 1440 wattsis delivered evenly to the other four elements. Because the convectionfan is generally “on”, the total power consumption may reach 1500 watts.In the bake mode, the default temperature is 350 Fahrenheit (optionallydelivered at least in part by true intermediate power) and the defaultcooking time is 30 minutes. Both of these values may be subsequentlyadjusted by the user, even in mid-cycle. In the bake mode, the frozenfood selector control may be disabled and the displayed symbol 605 maybe caused to flash to indicate than an improper selection has been made.In some embodiments, the delivery of power may be biased toward thebottom elements for all or a portion of the cooking cycle. When theStart button is pressed in Bake mode, the oven preheats until theselected temperature has been reached. PREHEATING flashes on thedisplay, and an audible sound then indicates that the oven has reachedthe selected temperature, and the timer starts to count downautomatically.

Roast Mode

When the roast mode has been selected, power is preferably deliveredevenly to all of the heating elements except for the top middle which isoff. When the Start button is pressed in the Roast mode, the ovenpreheats until the selected temperature has been reached. PREHEATINGflashes on the display, and an audible sound then indicates that theoven has reached the selected temperature, and the timer starts to countdown automatically. The power delivery to the elements 1440 watts andutilisation of the 60 watt convection fan results in a total powerconsumption of about 1500 watts. Power may be biased toward the bottomelements during all or a part of the cooking cycle. In the roast mode,the default temperature is 350 degrees Fahrenheit (optionally deliveredat least in part by true intermediate power) and the default roastingtime is 60 minutes. Both of these values may be adjusted by the user preor mid-cycle. The maximum time permitted in the roast mode is two hours.In the roast mode, the frozen food function is disabled and the displaysymbol 605 may be caused to flash so as to indicate that an improperselection has been made. In preferred embodiments, the default for theconvection fan is “on”.

Broil Mode

Three different broil preferences may be set using thetemperature/darkness dial 515. If the user sets the broil to (e.g.) 300degrees Fahrenheit, power delivery to the top front and top rearelements is set to about 310 watts each. The top middle element will becycled with the triac or relay to achieve an average of about 380 watts.This results in an overall power delivery of about 1000 watts. Thedefault time is set to 15 minutes with a maximum time of 20 minutes. Thefrozen food preference control is disabled. The default for theconvection feature is “off” but a user can use the convection control520 to activate it. Cooking times are not adjusted by the microprocessorif the convection feature is selected.

If the user sets the broil setting of (e.g.) 400 Fahrenheit using thetemperature/darkness control 515, only the top elements are used. Thefront and back elements are powered to 390 watts and the top middleelement is cycled to achieve an average power of 470 watts. This resultsin an average power delivery of 1250 watts. The default cooking time is15 minutes with a maximum time of 20 minutes. The frozen food andconvection features operate the same as when the user sets the broil to300 Fahrenheit.

The user may also select a third discreet broil temperature of (e.g.)450 or 500 degrees Fahrenheit. Thus, it will be appreciated that theuser is effectively presented with three broil settings, effectivelybeing low broil, medium broil and high broil, each designated by adifferent display of temperature. The display can be configuredaccordingly to display e.g. Low, Medium or High instead of a specifictemperature. In the high broil setting, all three top elements are usedand each is used to its maximum power rating. The bottom elements arenot used. The total power delivery is thus about 1450 watts. The defaultand maximum times, frozen food and convection features are handled inthe same way as the other broil settings.

Pizza Mode

When the pizza mode has been selected, the user can select a number ofdifferent pizza sizes (diameters) using the time/load size dial 516. Forexample, a user may be able to select from 6 inch, 8 inch, 10 inch, 12inch or 13 inch pizza sizes. The 12 inch size is the preferred default.The default cooking time for the 12 inch default pizza is 15 minuteswith no oven preheating. Cooking times vary, for example, from 12minutes for a six inch pizza through to 15 minutes, 30 seconds for a 13inch pizza. The frozen food setting default is “on” for pizza. If theuser elects to disable the frozen food setting by pressing the frozenfood button 522, the cooking time is adjusted downward, for example, bytwo minutes. In the pizza mode, the convection default is “on”. When inthe pizza mode, the top middle element is off but the other elements areon and powered equally. In preferred embodiments, each element ispowered to 360 watts (optionally delivered at least in part by trueintermediate power) and because the 60 watt fan is on, the total powerconsumption is about 1500 watts. The maximum cooking time allowed in thepizza mode is 40 minutes. The default cooking temperature in the pizzamode is 450 degrees Fahrenheit.

The thermistor 870 in the oven may provide oven temperature feed backinformation that allows the processor 801 to compensate for the internaltemperature of the oven, by reducing the cooking time as required.

When the Start button is pressed in the Pizza mode, the oven preheatsuntil the selected temperature has been reached. PREHEATING flashes onthe display, and an audible sound then indicates that the oven hasreached the selected temperature, and the timer starts to count downautomatically.

Cookies Mode

When the cookies mode has been selected by a user, the top middleelement is off but the other elements are powered equally to about 360watts. With the inclusion of the convection fan, the total powerconsumption is about 1500 watts. The default cooking temperature forcookies is 350 degrees Fahrenheit (optionally delivered at least in partby true intermediate power) but this can be modified by the user. In thecookies mode, the default baking time is 12 minutes (after the ovenpreheats to the selected cooking temperature). The preheat time istypically five minutes. If the frozen food preference is selected by theuser, the cooking time is adjusted upward by about 2 minutes.

When the Start button is pressed in the Cookies mode, the oven preheatsuntil the selected temperature has been reached. PREHEATING flashes onthe display, and an audible sound then indicates that the oven hasreached the selected temperature, and the timer starts to count downautomatically.

Reheat Mode

When the reheat mode has been selected by a user, the top middle elementis off and the other elements are powered equally to approximately 360watts each. Because the convection fan is defaulted to “on” the totalpower consumption is about 1500 watts. In the reheat mode, the defaultcooking time is 15 minutes with a maximum setting of one hour. Thedefault temperature in the reheat mode is 350 degrees Fahrenheit(optionally delivered at least in part by true intermediate power).

Keep Warm Mode

When a user selects the keep warm mode, the top middle element is offand the other elements are powered equally to 360 watts each. Thedefault warming temperature is 160 degrees Fahrenheit and the defaultwarming time is 60 minutes. The maximum keep warm time is two hours. Inthe keep warm mode, the frozen food function is disabled. The convectiondefault is off but may be activated by the user.

The thermistor 870 in the oven may provide oven temperature feed backinformation that allows the processor 801 to compensate for the internaltemperature of the oven.

As shown in FIG. 13 the printed circuit board 1251 previously disclosedwith reference to FIG. 8 may contain zero crossing sensor circuitry1252. The zero crossing sensor 1252 uses a diode and transistorarrangement with suitable resistors and capacitors so as to provide asignal 1253 to the oven's integrated circuit type controller 1254 everytime the wave of the 12 AC power supply to the PCB reaches zero volts.This provides the controller 1254 with signal information from which thefrequency of the input power can be determined. Given the zero crossingsignal, the controller 1254 can then drive the triacs and associatedcircuits to manipulate the wave form of the AC power that is supplied tothe one or more heating elements that are dimmed, that is, adapted todeliver true intermediate power. Schematic representations of the ACwave forms that result in dimming or true intermediate power 1255, assupplied by the PCB 1252 to the elements are exemplified in FIGS. 14A,14B, 14C, 14D, 14E.

As shown in FIG. 14A, the wave form of the AC power supplied to the topelement 1301 and to the bottom element 1302, during toasting, is uniformand generally represents the maximum power available to an element atany given time. In a bread toasting mode, it is advantageous to supplythe maximum available power so that the bread browns quickly withoutdrying out.

In FIG. 14B wave forms are illustrated for the top element 1303 and thebottom element 1304 during, for example, a bake mode. As suggested byFIG. 14B an AC wave group comprising seven full and uninterrupted waves1305 is followed by an interruption equivalent to a duration of two wavelengths 1306 during which the controller 1204 reduces the power outputto zero. Thus out of a duration of nine consecutive wave lengths, onlyseven continuous wave lengths are provided. In preferred embodiments,the top element uses this scheme 1303 while the scheme 1304 of thebottom element has eight continuous full power waves 1307 followedimmediately by a one wave length duration interruption in power 1308.Accordingly, the bottom element is producing more true intermediatepower than the top element.

As suggested by FIG. 14C the bottom element in a roasting mode issupplied with a continuous maximum power wave form 1309. In this sameroasting mode, the wave form of the top element 1310 comprises a wavegroup of seven continuous AC cycles 1311 followed by an intervalequivalent to three wave lengths of power interruption 1312.Accordingly, the bottom element can be seen operating in full powerwhile the top element only receives seven out of every ten cycles of ACpower.

A typical cooking cycle associated with a bake mode is illustrated inFIG. 15. As suggested by this graph, the oven's (actual or inferredcavity) temperature begins at room temperature 1501 and rises evenlyuntil the oven's thermistor detects a temperature that is equivalent toan oven 72 a target oven centre temperature 1502. In this example, thetarget temperature 1502 is 210 C. During this pre-heating phase 1503both the upper and lower elements are on at a true intermediate power.In this example, the top elements are using 720 W and the bottomelements are consuming 720 W giving a total power draw of 1440 W, forexample, provide gentle heat and to conform to regulatory requirements.When the measured oven cavity temperature reaches the target temperature1504 the top and bottom elements cycle on and off together, providing anaverage centre temperature, over time that equates to the targettemperature 1502.

As shown in FIG. 16, a typical toasting cycle begins with the thermistormeasured (inferred) oven cavity temperature being at room temperature1601. During toasting, two top elements and two bottom elements are atfull power delivering a total of 1800 W until this first toast cyclefinishes 1602. The duration of the first toast cycle 1603 is determinedby the oven's microprocessor in a predictive manner taking into accountuser inputs relating to the number of pieces of toast (oven load), theinitial oven cavity temperature and the level of colour or darknessselected by the user. The graph in FIG. 16 also shows the fall in ovencavity temperature 1604 that occurs when the door is opened and thecooked toast is removed. In this example, a second toast cycle 1605 iscommenced with an initial over cavity temperature 1606 that is higherthan room temperature. This second cycle also provides 1800 W of cookingpower, delivering full power to two top and two bottom elements. Thisfull power phase of the toast cycle continues until the oven cavitytemperature reaches a pre-established first threshold that is programmedinto the microprocessor. In this example, the first thresholdtemperature is 210 C. When this first threshold is exceeded, the powerto the two top and two bottom elements is reduced to a total power of1620 W, divided equally between the top and the bottom elements. Theduration of this second user initiated toasting cycle is determined bythe oven's microprocessor, in a predictive matter, taking into accountthe oven's starting temperature, the number of slices requested by theuser (oven load) and the level of darkness or colour requested by theuser. This reduced power phase 1606 continues until the oven centretemperature reaches a level just short of a second threshold 1607. Inthis example, the second threshold is 250 C. Just before the secondthreshold temperature, the top elements begin to turn on and off,simultaneously, at a time interval ranging between 5 and 20 seconds soas to keep the oven centre temperature below the second threshold. Inthis way, overcooking the toast in a hot oven is prevented while stillproviding some degree of radiant energy to continue the bread toastingor colouration process.

The graph of FIG. 17 illustrates aspects of the bagel mode. Cookingbagels in a bagel mode occurs over a time duration 1701 that isdetermined by the microprocessor, in a predictive manner, taking intoconsideration the number of bagel pieces being cooked (oven load), theinitial temperature (initially room temperature) and the level of colouror darkness requested by the user. The first bagel cooking phase in thecooking cycle 1702 occurs for approximately 150 seconds with full powerbeing delivered to two top elements and two bottom elements. Thisprovides a maximum power cooking phase delivering 1800 W. At the end ofthe first phase 1703 (about 150 seconds) the bottom elements are turnedoff and the top elements continue cooking at an increased combined powerof 1440 W using a third element. This second phase continues until theend of the first cycle 1705. The graph of FIG. 17 then illustrates thedrop in oven centre temperature 1706 caused by the opening of the ovendoor and the removal of the bagels from within. In this example, asecond bagel toasting cycle begins at a temperature that is elevatedfrom room temperature 1707. Initiation of the second cycle causes aphase similar to the first phase of the first cycle 1702, that is, about150 seconds with the two top and two bottom elements delivering a totalof 1800 W, that is, the top pair and the bottom pair of elements eachdelivering 900 W per pair. The duration of the second bagel toastingcycle is also determined by the microprocessor, in a predictive mannertaking into account the initial oven centre temperature 1707, the ovenload and the darkness selected by the user. A third bagel toasting cycleis shown as beginning at an initial temperature 1708 that is higheragain than the starting point for the second toasting cycle. However, ina bagel mode toasting cycle where the oven centre temperature reaches apredetermined threshold 1709, the bottom elements are turned off and thetop elements continue cooking at power of 1440 W using the fifth ovenelement. Thus, the first phase 1710 of this third cycle is truncated,terminating when the threshold temperature 1709 is achieved. In thisexample, the threshold temperature is 210 C. Where the cooking cycle islong, for example, when the oven load is high and the darkness settingis high the three top elements (or two top elements if there are onlytwo) will cycle from on to off every 5-20 seconds to keep the ovencentre temperature below a second predetermined threshold 1711. In thisexample, the second threshold 1711 is 250 C.

While the present invention has been disclosed with reference toparticular details of construction, these should be understood as havingbeen provided by way of example and not as limitations to the scope orspirit of the invention.

What is claimed is:
 1. A countertop toaster oven, comprising: aninternal compartment; a door for the compartment; a first heatingelement and a second heating element being top heating elements, locatedadjacent to a ceiling of the compartment; a third heating element and afourth heating element being lower heating elements, located along afloor of the compartment; an additional fifth heating element beinglocated between the top heating elements, the fifth element having ahigher maximum wattage than the top heating elements; a controllercoupled to the first heating element, second heating element, thirdheating element, fourth heating element and fifth heating element; thecontroller operates one or more heating elements to provide a variablewattage including one or more operational wattages that is, for at leasta portion of a heating cycle, intermediate between zero power and fullpower; a user interface coupled to the controller, wherein upon useroperation of the interface an oven mode is selected from one or morepredetermined oven modes; the first heating element, second heatingelement, third heating element and fourth heating element beingcontrolled by the controller to provide variable wattage in accordancewith the selected oven mode; and wherein the controller operates thefifth heating element independently of the top heating elements.
 2. Thetoaster oven according to claim 1, wherein the controller operates thefifth heating element independently of the top heating elements and thelower heating elements.
 3. The toaster oven according to claim 2,wherein the controller does not operate the fifth heating element at thesame time that the lower heating elements are operated.
 4. The toasteroven according to claim 1, wherein the controller regulates the heatingelements using triacs to control thermal output; and the fifth heatingelement is controlled independently of the top heating elements and thelower heating elements; and wherein the first heating element is locatedcloser to the door then the second heating element, and the firstheating element is controlled to operate at a higher thermal output thanthe second heating element.
 5. The toaster oven according to claim 4,wherein the controller does not operate the fifth heating element at thesame time that the lower heating elements are operated; and wherein thetop heating elements are simultaneously activated; and wherein the lowerheating elements are simultaneously activated.
 6. The toaster ovenaccording to claim 1, wherein the internal compartment comprises aplurality of opposing pairs of fixtures for supporting one or moreremovable racks at predetermined heights within the compartment.
 7. Thetoaster oven according to claim 1, wherein the internal compartmentcomprises a plurality of opposing pairs of fixtures for supporting oneor more removable racks at predetermined heights within the compartment;the predetermined heights being associated with one or more of thepredetermined oven modes; wherein a rack height is user selected inaccordance with the selected oven mode.
 8. The toaster oven according toclaim 1, the toaster oven comprises a user interface for selecting anoven mode from the set comprising: toast mode, bake mode, and grillmode.
 9. The toaster oven according to claim 8, wherein the internalcompartment comprises a plurality of opposing pairs of fixtures forsupporting one or more removable racks at predetermined heights withinthe compartment; the predetermined heights being associated with one ormore of the predetermined oven modes.
 10. The toaster oven according toclaim 9, wherein internal compartment has at least three opposing pairsof fixtures for supporting a removable rack at a selected predeterminedheight within the compartment; wherein the rack height is selected inaccordance with the selected oven mode, the rack height being selectedat a low-position when operating in the bake mode, the rack height beingselected at a mid-position when operating in the toast mode, and therack height being selected at a high-position when operating in thegrill mode; wherein the first heating element, the second heatingelement, and the fifth heating element are located above the rack whenin the high-position; and wherein the third heating element and thefourth heating element are located below the rack when in thelow-position.
 11. The toaster oven according to claim 10, wherein onlythe first heating element, the second heating element, the third heatingelement and the fourth heating element are active in the toast mode;only the first heating element, the second heating element, the thirdheating element and the fourth heating element are active in the bakemode; and only the first heating element, the second heating element andthe fifth heating element are active in the grill mode.
 12. The toasteroven according to claim 10, wherein a perforated metal shield isinterposed between the fifth heating element and food being cooked. 13.The toaster oven according to claim 12, wherein only the first heatingelement, the second heating element, the third heating element and thefourth heating element are active in the toast mode; only the firstheating element, the second heating element, the third heating elementand the fourth heating element are active in the toast mode; and onlythe first heating element, the second heating element and the fifthheating element are active in the grill mode.